What the Grade Numbers Mean
The grade number represents the minimum silicon content in the alloy. For example, FeSi75 means about 75 percent silicon, FeSi72 about 72 percent, and FeSi65 about 65 percent. Higher silicon content usually results in stronger deoxidizing ability and more stable alloying performance. These grades exist because different steel products require different silicon levels and cost structures.
Most Commonly Used Grades in Steelmaking
FeSi75 is the high-performance grade, preferred for higher-quality steels. FeSi72 is economical and suitable for general steelmaking. FeSi65 is a cost-effective option for basic steel and foundry applications. Among these, FeSi75 is the most popular internationally because of its consistent silicon recovery and lower impurity range. FeSi72 follows closely because it offers similar performance at a lower cost, making it attractive for mills producing standard carbon steel.
Other Grades
Some regions use additional classifications. FeSi90 is a high-silicon alloy, less common in trade. FeSi45 is a low-silicon alloy for specific uses. FeSiMg is a magnesium-containing ferrosilicon for nodular cast iron. Atomized or milled FeSi is classified by particle shape rather than silicon content. While FeSi75 and FeSi72 dominate global trade, these specialty grades serve niche applications such as casting, magnesium treatment, and powder metallurgy.
How Grades Influence Steel Quality
The grade selected affects deoxidation efficiency, silicon recovery, impurity control, and alloy performance. Higher grades remove oxygen more effectively, yield more stable results, and typically have lower and more consistent impurities. Lower grades can still be used effectively, but they may require larger addition volumes or produce more metallurgical variability.
How to Choose the Right Grade
Buyers often base their choice on three factors: steel grade requirements (high-strength or clean-steel production typically requires FeSi75), cost considerations (FeSi72 and FeSi65 help reduce cost without major performance loss for general steel), and impurity sensitivity (if phosphorus, sulfur, or aluminum levels must be controlled strictly, FeSi75 is safer). Many factories actually mix grades, using FeSi75 for higher-end products and FeSi72 for ordinary steel, to balance performance and cost.
Frequently Asked Questions
What does the number in FeSi75 mean? The minimum silicon content, about 75 percent.
Which ferrosilicon grade is most used internationally? FeSi75, for its consistent silicon recovery and lower impurity range.
What is FeSiMg? A magnesium-containing ferrosilicon used for nodular cast iron.
Can grades be mixed? Yes, many factories use FeSi75 for higher-end products and FeSi72 for ordinary steel.
